A non-nematicidal composition comprises at least one glucan and/or at least one fucan which act individually or synergistically with mannitol to reduce losses in crop yield and marketable grade caused by the infestation of growth media with plant pathogenic nematodes, to levels equivalent to those achieved with commercial nematicides, but without posing a risk to the ecosystem or user. In some cases the composition comprises at least one glucan, at least one fucan and at least one mannitol which may be in a weight/weight ratio of approximately 1:2:3 of at least one glucan:at least one fucan:at least one mannitol or between approximately 1:1:1 to 1:1:3 of at least one glucan:at least one fucan:at least one mannitol.